Various factors limit the efficiency and functionality of traditional power supply devices used for powering and/or charging electronic devices (e.g., cellular telephones and portable media devices). For example, most traditional power supply devices convert an alternating current (“AC”) input to a regulated direct current (“DC”) output whenever the power supply device is plugged into a power outlet (e.g., an outlet coupled with a power grid). This wastes power because the power supply continuously provides a regulated power signal even if it is not powering an electronic device. Moreover, it is difficult to design efficient power supply devices for portable electronic devices due to size limitations associated with portability. Additionally, many portable electronic devices have limited interfaces for coupling with a power supply device so it can be difficult for a traditional power supply device to determine when it is coupled with an electronic device. For example, a portable electronic device may include a connector with only a power signal wire and a ground wire, and therefore, no extra wires can be used by a traditional power supply device to determine when it is coupled with the electronic device.